NOx SENSING SYSTEM HAVING NOx SENSOR AND METHOD FOR DETERMINING A NOx CONCENTRATION UTILIZING THE NOx SENSOR

Abstract

A NOx sensing system having a NOx sensor and a method for determining a NOx concentration utilizing the NOx sensor are provided. The NOx sensor utilizes a second chamber communicating with ambient atmosphere with ambient oxygen for allowing an electrochemical cell to accurately measure an oxygen concentration in a first chamber communicating with an exhaust stream to more accurately control the oxygen concentration in the first chamber, without disassociating NOx therein. The more accurate control of the oxygen concentration in the first chamber, subsequently allows for a more accurate measurement of the NOx in the exhaust system.

1 . A NOx sensor, comprising:
 a housing having a first chamber configured to receive NOx and oxygen from an exhaust stream, a second chamber configured to communicate with ambient atmosphere, a third chamber communicating with the first chamber, and a fourth chamber communicating with the third chamber;   a first electrochemical pumping cell disposed between the first chamber and the second chamber, the first electrochemical pumping cell configured to pump oxygen from the first chamber into the second chamber such that an oxygen partial pressure in the first chamber is maintained greater than a first predetermined oxygen partial pressure level, the NOx and remaining oxygen in the first chamber migrating from the first chamber to the third chamber;   a second electrochemical pumping cell disposed between the third chamber and the second chamber, the second electrochemical pumping cell configured to pump oxygen from the third chamber to the second chamber such that an oxygen partial pressure in the third chamber is maintained less than a second predetermined oxygen partial pressure level, the NOx in the third chamber migrating to the fourth chamber; and   a third electrochemical pumping cell communicating with the fourth chamber, the third electrochemical pumping cell configured to decompose the NOx in the fourth chamber, wherein an output current of the third electrochemical pumping cell indicates a concentration of NOx in the fourth chamber.   
   
   
       2 . The NOx sensor of  claim 1 , wherein the first electrochemical pumping cell has a first platinum electrode communicating with the first chamber and a second platinum electrode communicating with the second chamber. 
   
   
       3 . The NOx sensor of  claim 1 , wherein the second electrochemical pumping cell has a platinum and gold electrode communicating with the third chamber and a platinum electrode communicating with the second chamber. 
   
   
       4 . The NOx sensor of  claim 1 , wherein the third electrochemical pumping cell has a rhodium electrode communicating with the fourth chamber and a platinum electrode communicating with the second chamber. 
   
   
       5 . The NOx sensor of  claim 1 , further comprising a reference electrochemical cell disposed between the first chamber and the second chamber, the reference electrochemical cell outputting a voltage indicative of the oxygen partial pressure in the first chamber. 
   
   
       6 . A method for determining a concentration of NOx utilizing a NOx sensor, the NOx sensor having a housing with a first chamber configured to receive NOx and oxygen from an exhaust stream, a second chamber configured to communicate with ambient atmosphere, a third chamber communicating with the first chamber, and a fourth chamber communicating with the third chamber, the NOx sensor further having a first electrochemical pumping cell disposed between the first chamber and the second chamber, the NOx sensor further having a second electrochemical pumping cell disposed between the third chamber and the second chamber, the NOx sensor further having a third electrochemical pumping cell communicating with the fourth chamber, the method comprising:
 pumping oxygen from the first chamber into the second chamber utilizing the first electrochemical pumping cell such that an oxygen partial pressure in the first chamber is maintained greater than a first predetermined oxygen partial pressure level, the NOx and remaining oxygen in the first chamber migrating from the first chamber to the third chamber;   pumping oxygen from the third chamber to the second chamber utilizing the second electrochemical pumping cell such that an oxygen partial pressure in the third chamber is maintained less than a second predetermined oxygen partial pressure level, the NOx in the third chamber migrating to the fourth chamber; and   decomposing the NOx in the fourth chamber utilizing the third electrochemical pumping cell, wherein an output current of the third electrochemical pumping cell indicates the concentration of NOx in the fourth chamber.   
   
   
       7 . The method of  claim 6 , wherein the NOx sensor further comprises a reference electrochemical cell disposed between the first chamber and the second chamber, the method further comprising outputting a voltage indicative of the oxygen partial pressure in the first chamber utilizing the reference electrochemical cell. 
   
   
       8 . A NOx sensing system, comprising:
 a NOx sensor having a housing having a first chamber configured to receive NOx and oxygen from an exhaust stream, a second chamber configured to communicate with ambient atmosphere, a third chamber communicating with the first chamber, and a fourth chamber communicating with the third chamber, the NOx sensor further having a first electrochemical pumping cell disposed between the first chamber and the second chamber, the first electrochemical pumping cell configured to pump oxygen from the first chamber into the second chamber such that an oxygen partial pressure in the first chamber is maintained greater than a first predetermined oxygen partial pressure level, the NOx and remaining oxygen in the first chamber migrating from the first chamber to the third chamber, the NOx sensor further having a second electrochemical pumping cell disposed between the third chamber and the second chamber, the second electrochemical pumping cell configured to pump oxygen from the third chamber to the second chamber such that an oxygen partial pressure in the third chamber is maintained less than a second predetermined oxygen partial pressure level, the NOx in the third chamber migrating to the fourth chamber, the NOx sensor further having a third electrochemical pumping cell communicating with the fourth chamber, the third electrochemical pumping cell configured to decompose the NOx in the fourth chamber;   a first voltage source configured to supply a variable voltage to the first electrochemical pumping cell, in response to a control signal;   a first current sensor configured to output a first signal indicative of an amount of current being output by the first electrochemical pumping cell, the first signal being indicative of an oxygen concentration in the first chamber;   a second voltage source configured to supply a voltage to the third electrochemical pumping cell;   a second current sensor configured to output a second signal indicative of an amount of current being output by the third electrochemical pumping cell, the second signal being indicative of a NOx concentration in the fourth chamber; and   a controller operably coupled to the first voltage source, the first current sensor and the second current sensor, the controller configured to generate the control signal received by the first voltage source based on the first signal from the first current sensor, the controller further configured to receive the second signal and to determine a NOx concentration value indicative of the NOx concentration in the fourth chamber based on the second signal, the controller further configured to store the NOx concentration value in a memory device.   
   
   
       9 . The NOx sensing system of  claim 8 , wherein the first electrochemical pumping cell of the NOx sensor has a first platinum electrode communicating with the first chamber and a second platinum electrode communicating with the second chamber. 
   
   
       10 . The NOx sensing system of  claim 8 , wherein the second electrochemical pumping cell of the NOx sensor has a platinum and gold electrode communicating with the third chamber and a platinum electrode communicating with the second chamber. 
   
   
       11 . The NOx sensing system of  claim 8 , wherein the third electrochemical pumping cell of thee NOx sensor has a rhodium electrode communicating with the fourth chamber and a platinum electrode communicating with the second chamber. 
   
   
       12 . The NOx sensing system of  claim 8 , wherein the NOx sensor further comprises a reference electrochemical cell disposed between the first chamber and the second chamber, the reference electrochemical cell outputting a voltage indicative of the oxygen partial pressure in the first chamber.